1. Field of the Invention
This invention relates to a non-fixing type image receiving sheet which is formed into an uneven surface and to which a toner adheres in a removable manner, an image forming method, and an image forming apparatus.
2. Description of Prior Art
(Fixing Type Image Receiving Sheet)
In a printer which is used as an outputting means for personal computer, at present, a generally typical printing method is an electro-photography method in which toner particles are thermally fixed on an image receiving sheet comprising such as a paper or a plastic material, or an ink jet method in which an ink is dryly fixed on the image receiving sheet.
In each fixing method described above, a time is required for printing, an electricity bill and consumables such as the ink become necessary, so that a running cost is required. In addition, measures for decreasing an energy of the printer and decreasing consumption of paper are required in view of recent tendency in reduction of environmental load.
On the other hand, a paper outputted from the printer is necessary temporarily. However, it is usual that the paper becomes unnecessary and disused immediately after the paper is glanced once.
(Non-fixing Type Image Receiving Sheet)
In contrast with the above-mentioned methods, a method is generally known in which a transferred paper is reused. As a method for separating the toner from the transferred paper, for instance, there are known a method in which the transferred paper is passed through between a pair of heated rollers so as to melt and exfoliate the solidified toner, and a method in which the ink is removed by utilizing water solution such as surface active agent.
However, a large volume of energy is required for heating and for removing penetrating water content. In addition, the removed toner can not be reused because it is molten and solidified.
In order to solve such a problem, Published Patent Application (KOKAI) No. 43,682 is proposing a method in which fine projections are dispersedly formed on a surface of the image receiving sheet, a toner image is transferred on the surface of the image receiving sheet having the many fine projections and then fixed by being pressed to form an image, and the toner is separated from the image receiving sheet by means of a mechanical method, thus the image receiving sheet and the toner become reusable.
A mechanical means such as brushing etc. becomes popular as a means for removing the toner from the image receiving sheet. However, it is difficult to completely remove the toner so as not to leave contamination on the non-fixing type image receiving sheet having the many fine projections as describe above, by using the mechanical means only. In other words, toner particles remain around roots of the projections even when mechanically cleaning them by brushing, and the toner particles falling in concave portions become impossible to be removed when these fine concave portions exist.
Independently from the mechanical toner removing means, there is a measure for absorbing and removing the toner electrostatically by utilizing a magnetic brush. Namely, this method is one in which a toner collecting magnetic brush is charged to a polarity opposite to that of charged polarity of the toner, the toner is absorbed to the magnetic brush by electrostatic absorption, thus the toner is removed from the surface of the image receiving sheet.
(Image Forming Apparatus)
FIG. 10 shows an example of a transferring apparatus (image forming apparatus) used for forming the toner image of the non-fixing type image receiving sheet, the apparatus is composed of a drum-type photoreceptor 127 and a transferring roller 128 facing on it. Around the photoreceptor 127, there are disposed a toner wiping-off (scratching-off) portion 131, an image charging portion 132, an exposing portion 133, and a developing portion 134; in an order from a transferring portion 130 contacting with the transferring roller 128 to a drum rotation direction side R.
The transferring roller 128 is applied with a bias to draw the toner particles. In order to carry out the transferring operation using such a transferring apparatus, the transferring roller 128 is applied with a bias to be charged to a positive polarity as shown by FIG. 11, when the toner particles are charged to a negative polarity. The toner particles charged to the negative polarity are drawn by the transferring roller 128 charged to the positive polarity and made adhere onto the surface of the image receiving sheet S.
3. Problems to be Solved by the Invention
According to the image receiving sheet as cited in Published Patent Application (KOKAI) No. 6-43682, the fine projection serves as a spacer at an upper part of the sheet so as to prevent the toner particles from adhering to a backside of an upper sheet which is placed upon the sheet surface. However, the projection does hardly fulfil its function to mechanically and securely retain the toner particles adhering to the sheet surface.
In addition, since the fine projections are formed only in the dispersed manner, there may be a case where the image receiving sheet on which the image has been formed is handled while the toner adheres to the fine projections of the image receiving sheet as it is. Although the toner is fixed to the projection by means of pressure treatment, the toner can be removed easily and mechanically from the image receiving sheet, so that fingers or sheet backsides may be contaminated when the sheet is touched with fingers or rubbed each other under piled condition.
Since the fine projections formed on the image receiving sheet are scattered independently as like a dotted pattern, they are apt to be deflected or deformed when an external force is applied. Therefore, foreign matters are apt to get in between the projections, the image is subjected to disturbance effect, and the toner image can not be protected enough.
A conventional image receiving sheet generally has a center line average roughness of sheet surface smaller than Ra=0.1 xcexcm, so as to provide a smooth flat surface. For this reason, Funderworth Force of the toner particle becomes too large so that an adhering force of the toner particle to the sheet surface becomes large. Therefore, a good cleanability (toner removability) can not be obtained and recycling of the sheet may be prohibited. Further, since the center line average roughness Ra is small, a regular reflection light quantity (brilliance) will become too large and the image may not be seen well.
Even when the cleaning is done utilizing the electrostatic absorption by the magnetic brush, a carrier of the magnetic brush and the sheet surface layer (media) slide contacting each other, during the cleaning operation, to produce a friction charge on the sheet surface layer (or toner) so that a charge quantity on the sheet surface layer will increase.
When a conductive carrier is equipped for the carrier of the magnetic brush, an increased charge can be relieved from the conductive carrier to some extent. However, when an insulated resin carrier is equipped therefor, there is no path to let the above charge leak so that the charge quantity on the sheet surface layer will increase suddenly to cause an increase in a force to absorb the toner. For this reason, the removal ability of toner particles will decrease.
As illustrated in FIG. 10 and FIG. 11, in a method or an apparatus for carrying out the transferring operation by utilizing only the drawing effect of toner particles through means of the charge of the transferring roller 128, the transferring roller is located apart from the toner particles on the surface of photoreceptor with a distance longer than a thickness of the image receiving sheet. Thereby, its electric field is weakened so that there is a limit in improving its transferability and retentivity by controlling the applied voltage only.
1. Objects of the Invention
Objects of inventions are to provide an image receiving sheet which can be used repeatedly, to improve a mechanical retentivity as compared with the image receiving sheet described in Published Patent Application (KOKAI) No. 6-43682, and to improve a desired property as demanded by consumers with regard to properties such as a toner retentivity including electric factor, a toner transferability and a cleaning ability (toner removability).
An object of the invention is to improve three properties of the electric toner: the retentivity, the toner transferability and the cleanability (toner removability), as a whole.
An object of the invention is to further improve the above-mentioned three properties in all.
An object of the invention is to further improve particularly the transferability and the retentivity.
An object of the invention is to provide an image receiving sheet which can be used repeatedly, to improve a mechanical retentivity as compared with the image receiving sheet described in Published Patent Application (KOKAI) No. 6-43682, and to improve even the cleanability (toner removability).
An object of the invention is to further improve the mechanical retentivity.
Other objects of the invention are to provide an image receiving sheet which can be used repeatedly, and to improve the retentivity of toner particles and the cleanability (toner removability).
Other objects of the invention are to improve the transferability and retentivity of toner particles in the image forming method and image forming apparatus of the non-fixing type image receiving sheet.
2. Solution for the Problems
(1) In order to accomplish the above objects, the invention is characterized by that, in the non-fixing type image receiving sheet to which toner particles are made adhere in a removable manner, a large number of concave portions accepting toner particles and a large number of convex portions protecting toner particles are formed on a surface of the image receiving sheet, and a sectional structure of the image receiving sheet is composed of a multilayer structure which includes at least a sheet surface layer having the above concave portions and convex portions and a sheet core layer.
(2) The invention according to an embodiment is characterized by that, in the non-fixing type image receiving sheet, volume resistivities of respective layers are different from each other.
(3) The invention according to another embodiment is characterized by that, in the non-fixing type image receiving sheet, a volume resistivity of the sheet surface layer is larger than a volume resistivity of the sheet core layer.
(4) The invention according to yet another embodiment is characterized by that, in the non-fixing type image receiving sheet, a volume resistivity of the sheet surface layer is set to 1012 xcexa9.cm or larger and a volume resistivity of the sheet core layer is set to 104 xcexa9.cm or larger and to 1010 xcexa9.cm or smaller.
(5) The invention according to another embodiment is characterized by that, in the non-fixing type image receiving sheet, the concave portion forming the above uneven surface is formed into a grooved shape and the convex portion is formed into a convex stripe extending along the grooved concave portion.
(6) The invention according to another embodiment is characterized by that, in the non-fixing type image receiving sheet to which toner particles are made adhere in a removable manner, a large number of concave portions accepting toner particles and a large number of convex portions protecting toner particles are formed on the surface of the image receiving sheet, and a center line average roughness Ra of the surface of the image receiving sheet is set to 0.2 xcexcm or larger and to 1.0 xcexcm or smaller.
(7) The non-fixing type image receiving sheet is characterized by that, in the non-fixing type image receiving sheet, the concave portion composing the above uneven surface is formed into a grooved shape, and the convex portion is formed into a ridged-shape convex stripe extending along the grooved-shape concave portion.
(8) The invention according to another embodiment is characterized by that, in the non-fixing type image receiving sheet to which toner particles are made adhere in a removable manner, a large number of concave portions accepting toner particles and a large number of convex portions protecting toner particles are formed on the surface of the image receiving sheet, and the surface of the image receiving sheet forming the concave portion and convex portion is made of high-molecular compound including fine particles of metal oxide.
(9) The invention according to another embodiment is characterized by that, in the non-fixing type image receiving sheet, a content of the fine particles of metal oxide is set to 0.1 g through 2 g per square meter of the image receiving sheet.
(10) The invention according to another embodiment is characterized by that, in the non-fixing type image receiving sheet, fine particles of zinc oxide, titanium oxide or alumina are contained for use as the fine particles of metal oxide.
(11) The invention according to another embodiment is characterized by that, in the non-fixing type image receiving sheet, fine particles of calcium carbonate or silica are contained in place of the metal oxide.
(12) The invention according to another embodiment is characterized by that, in the image forming method for the non-fixing type image receiving sheet to which toner particles are made adhere in a removable manner, a large number of concave portions accepting toner particles and a large number of convex portions protecting toner particles are formed on the surface of the image receiving sheet, and the surface of the image receiving sheet is charged to a polarity opposite to the charged polarity of toner particles for serving as a pre-process, in advance of transferring the toner image to the image receiving sheet.
(13) The invention according to another embodiment is characterized by that, in the image forming apparatus for the non-fixing type image receiving sheet to which toner particles are made adhere in a removable manner, a large number of concave portions accepting toner particles and a large number of convex portions protecting toner particles are formed on the surface of the image receiving sheet, and there are installed two apparatuses: a transferring apparatus which transfers the toner image to the surface of image receiving sheet, and a sheet charging apparatus which charges the surface of the image receiving sheet to a polarity opposite to the charged polarity of the toner particles, in advance of the transferring process carried out by the transferring apparatus.
3. Advantages of the Inventions
As explained above, according to the invention of the present application, following advantages become obtainable.
(1) Since the non-fixing type image receiving sheet is used to which the toner particles are made adhere in a removable manner; the image receiving sheet can be reused, a consumption of paper can be reduced, an energy and expendable supplies as required for the fixing type becomes unnecessary, the toner collected from the image receiving sheet can be reused, so that a running cost can be minimized.
(2) Since a large number of concave portions for receiving the toner particles and a large number of convex portions for protecting the toner particles are formed on the surface of the image receiving sheet S; the toner particles are mechanically and securely held in the concave portion, the plural convex portions increase the above-mentioned mechanical holding ability, and the convex portions serve as spacers so that the convex portions can securely prevent foreign matters (such as fingers or other sheet backsides) from contacting with the sheet from upside and can improve the mechanical retentivity.
(3) When many concave portions and convex portions are formed on the sheet surface, and the sectional structure of image receiving sheet is formed at least into the multilayer structure including the sheet surface layer having the uneven surface together with the sheet core layer; the volume resistivity for each layer can be easily changed in relation to the transferability, the retentivity and the cleanability, thereby the image receiving sheet improved in its property can be provided according to demands of customers.
(4) When the volume resistivity xcfx811 of the sheet surface layer is made larger than the volume resistivity xcfx812 of the sheet core layer, results as listed for the sample sheets SP1 through SP8 in Table 2 are obtained, so that a possibility becomes large in making up the image receiving sheet having a good transferability, retentivity and cleanability.
(5) The volume resistivity xcfx811 of the sheet surface layer 2 is set to 1012 xcexa9.cm or larger and the volume resistivity xcfx812 of the sheet core layer 3 is set to 104 xcexa9.cm or larger and 1010 xcexa9.cm or smaller, it becomes possible that all of the image receiving sheets can securely present good transferability, retentivity and cleanability.
In concrete, sufficient transferring electric field can be obtained in the transferring region, thereby the transferability can be improved. In the cleaning region, the potential removing effect of the image receiving sheet can be made better at time of peeling-off of the toner particles and the cleanability can be improved, so that it becomes possible to form a stable image. In addition, when the image receiving sheets on which images have been formed are placed one upon another; an electrostatic shielding effect can be obtained, a toner absorbing force can be secured with respect to the sheet surface layer, and an image retentivity can be kept high.
(6) When the concave portion composing the uneven sheet surface is formed into the grooved-shape and the convex portion is formed into the ridged-shape (convex stripe) extending along the grooved concave portion, the mechanical retentivity is improved further and the image receiving sheet providing a high resolution and a high contrast can be realized.
(7) Since the center line average roughness Ra of the image receiving sheet is set to 0.2 xcexcm or larger and 1.0 xcexcm or smaller, a good cleanability can be obtained and an appropriate brilliance, which is hard to produce a brilliant after image, can be obtained as obvious from Table 3. In other words, the cycle stability can be improved and a visible image controlled in its brilliance can be obtained.
(8) Since the fine particles of metal oxide such as titanium dioxide or the fine particles of silica, calcium carbonate etc. are contained in the thermosetting or thermoplastic sheet surface layer; a good cleanability can be secured by releasing the overcharging caused by friction charging, while maintaining the toner particle retaining force produced by a proper electrostatic drawing force.
(9) The mechanical retentivity of toner particle can be improved especially by forming a number of concave portions and a number of convex portions on the sheet surface layer 2 as described above. However, even when these concave portions and convex portions disturb the cleaning operation utilizing the magnetic brush and the friction charging is apt to be produced, the overcharging can be properly released and the cleanability can be improved securely.
(10) When the content of fine particles of metal oxide such as titanium dioxide is set to 0.1 g to 2 g per square meter of the image receiving sheet, the effect of its cleanability becomes more remarkable.
(11) Since the surface of the image receiving sheet is charged (pre-charging) to the polarity opposite to the charged polarity of the toner by means of the sheet charging apparatus in the pre-process wherein the toner image is transferred to the image receiving sheet; the transferring electric field becomes substantially large so that the transferability is improved in the transferring process.
(12) Since the surface of the image receiving sheet is charged to the polarity opposite to the charged polarity of the toner particles, the toner particles can be held under electrostatic stable condition and the image retentivity can be improved because the charge exists at the surface side of the image receiving sheet.
(13) Since the image receiving sheet itself is charged, the toner particles adhere electrostatically and strongly to the sheet surface. Therefore, even if the image receiving sheets on which images are formed are placed one upon another, such a phenomenon (so-called a backside copying phenomenon) does not occur wherein the toner particles move to a backside of an opponent sheet.